Sudden cardiac death during heart failure is a major concern in the United States and other Western Nations. The broad long term objectives of this study are to understand the time course and impact of heterogeneous gap junction and extracellular space remodeling during heart failure. It has been recently demonstrated that gap junction functional remodeling precedes conduction velocity changes by approximately two weeks.1 Since conduction slowing is implicated as a mechanism of sudden cardiac death, and the relationship between gap junctions and conduction velocity is a topic of significant controversy and debate, it is imperative to understand all the mechanisms that modify this relationship. Even more broadly speaking, the gap junction-conduction velocity (Gj-8) relationship is important for understanding sudden cardiac death in diseases such as ischemia, hypertrophy, and heart failure, because all three are associated with gap junctional remodeling and altered conduction. If the extracellular space significantly modulates the gap junction conduction velocity relationship as preliminarily demonstrated in this application, then modulating the cardiac extracellular space may be a previously untapped therapeutic target for heart failure. Our approach to address this hypothesis will bring together three state of the art methodologies and associated experts. 1. Dr. Steven Poelzing (PI), an expert on quantifying the Cx43-conduction velocity relationship, will be responsible for demonstrating that pharmacologically modulating ventricular ECS modulates Gj-8 relationship in pharmacologic and genetic models of Cx43 functional down-regulation. 2. Dr. Mohamed Salama (collaborator), an expert on morphometric analysis of cell structure and the extracellular matrix, will be responsible for determining how the ex-vivo interventions implemented by Dr. Poelzing changes cell size and the ECS. 3. Finally, Dr. James Keener, an expert of mathematically modeling cardiac conduction will develop a model of cardiac conduction that includes electric-field coupling in addition to gap junctional coupling. This model will include all the data collected from Drs. Poelzing, and Salama. The mathematical model will be validated against all interventions proposed in the animal experiments. PUBLIC HEALTH RELEVANCE: Ventricular arrhythmias account for 80% of over 450,000 cases of sudden cardiac death that occur in the U.S. each year. While there is an established association between aberrant conduction and arrhythmias, the mechanisms of conduction failure in diseases such as heart failure and ischemia remain unknown. Interestingly, two common findings in heart failure and ischemia are an increased extracellular volume (i.e. edema) and impairment of intercellular coupling. The role of intercellular coupling is well researched, but controversial, and the role of the extracellular volume has been largely ignored until recently. The purpose of this proposal is to demonstrate that the extracellular space is an important determinant of risk for sudden cardiac death since it modulates the relationship between intercellular coupling and cardiac conduction. Modulating the extracellular space represents a novel therapeutic target for heart failure and sudden cardiac death.